Approach to Equilibrium in Weakly Coupled Non-Abelian Plasmas

We follow the time evolution of nonabelian gauge bosons from far-from-equilibrium initial conditions to thermal equilibrium by numerically solving an effective kinetic equation that becomes accurate in the weak coupling limit. We consider initial conditions that are either highly overoccupied or underoccupied. We find that overoccupied systems thermalize through a turbulent cascade reaching equilibrium in multiples of a thermalization time t(eq) approximate to 72./(1 + 0.12 log lambda(-1)) x 1/lambda T-2, whereas under-occupied systems undergo a bottom-up thermalization in a time t(eq) approximate to [34. +21.log(Q/T)]/(1 + 0.037 log lambda(-1)) x (Q/T)(1/2)/lambda T-2, where Q is the characteristic momentum scale of the initial condition. We apply this result to model initial stages of heavy-ion collisions and find rapid thermalization roughly in a time Qt(eq) less than or similar to 10 t(eq) less than or similar to 1 fm/c.